The plasma contact activation system can be viewed as initiating surface-mediated defense reactions. Thus, the biological role of this system is to be viewed primarily as participatory in the pathophysiological reactions to injury, including the coagulation, fibrinolytic, kinin-forming and complement systems, as well as specific interactions with neutrophils and platelets. We wish to delineate the role of two of the contact system proteins. HMW kininogen and kallikrein, in the biochemistry of the inflammatory action. We will probe the importance of proteolytic activation of HMW kininogen in its surface binding activity by using a fluorescent inhibitor assay which avoids proteolytic feedback. We will study the action of this cofactor to inhibit platelet calcium- activated cysteine proteases (calpains) by delineating the kinetics of the reaction and the formation of complexes. We will study genetically engineered inhibitors of contact enzymes, including alphalantitrypsin Pittsburgh and arginine substituted aprotonin. We will use monoclonal antibodies to probe functional domains of contact proteins, as well as to develop new immunochemical assays of neoantigens in enzyme-inhibitor complexes, activated enzymes and activation peptides. These new assays will be applied to patients with hypotensive septicemia, adult respiratory distress syndrome, and cardiopulmonary bypass. We will also further define the role of contact system enzyme, kallikrein as an agonist for stimulation of neutrophils. We will focus on the interaction of fibronectin with these enzymes, the binding of these proteins to neutrophils, and the effect of neutrophis elastase of contact system proteins. This combined biochemical, clinical and cell biological approach should further our understanding of the role of the contact system in inflammation.